The effect of total ionizing dose on the time-dependent breakdown characteristics of the high dielectric constant HfO₂-based gate dielectric used in nano-Metal-Oxide-Semiconductor(MOS) devices has been investigated. The MOS capacitor with HfO₂-based gate dielectrics is taken as the research object, a total dose ionization irradiation experiment of ⁶⁰Co-γ rays with different gate biases is carried out. The test results of current-voltage, capacitance-voltage and time-dependent dielectric breakdown characteristics of MOS capacitor before and after irradiation are compared. The results show that the damage characteristics of MOS capacitors are different under different irradiation bias conditions. Under positive bias irradiation, the gate current increases significantly at low gate voltage, and the slope of capacitance-voltage characteristic decreases. Under zero bias irradiation, the gate current and capacitance increase significantly at high forward gate voltage. Under negative bias irradiation, the gate current increases, the capacitance increases under high forward gate voltage while the capacitance slope decreases. The time-dependent breakdown voltage of the capacitor decreases significantly under all three bias conditions. This study provides a reference for the long-term reliability study of nano-MOS devices in radiation environments.